Brent said, “I
don't get the dual big battery configuration… I would rather have 5
gallons of fuel… Watch the ounces and the pounds take care of
themselves.”
Brent, Thanks for the feedback. In
general, I couldn’t agree with you more. However, with an ES the
practical choices are a 360 with the battery wherever you like (firewall), or a
550 with weight in the tail. For most of ES builders, the advantages of
the 550 (over the 360), outweigh the tradeoff of a few lbs of #2 wire and the sub-optimal
aft battery(ies) location.
5 gallons of fuel will not help. To
be effective in balancing CG, Moment is computed as Weight x moment Arm.
With fuel, the moment Arm is near the CG and thus the weight of the fuel is not
helpful from a CG standpoint. In fact, my understanding is that the fuel
is generally designed to be near the CG so that the CG doesn’t change
(much) as fuel is burned.
I’m not sure “scrutinizing
every ounce” has much “practical” CG relevance for most ES
builders either. The firewall, engine mount, strut, ect are all done by
the factory as part of the fastbuild and the rudder pedals and control sticks
are pretty much given asis. There are relatively few layups and/or
builder discretionary items in front of the CG (unless you’re adding
things up there). I did replace the nylaflow brake lines with DHLines
which are a bit heavier (wrong CG direction), but still lighter than SS.
I’m also planning on adding an engine pre-heat pad – which I think
is a requirement here in the North. I’m still undecided about
putting a landing light in the cowl versus the wing tips (which would be better
for CG). I’ve opted for the lighter composite MT prop, (versus the
commonly preferred heavier aluminum Hartzel). I’ve also moved the
boost pump 3’ rearward from standard ES firewall location and moved the
elevator A/P servo and O2 bottle to the tail and stayed with the std
non-pressurized windshield (lighter). I’ve also optimized the
engine hose lengths and fittings. Trying to scrimp with a few less Adel
clamps seems a poor FF safety tradeoff for perhaps a few oz. I’m
also searching for a good/accessible internal location for the brake fluid
reservoir (which could then be plastic vs the steel firewall version that comes
with the kit). However, for ease of maintenance I’ll probably end
up with the std reservoir/location. I’m not sure what else
(of any significance) I can alter in front of the CG, besides optimizing/minimizing
the weight of the equipment in the panel. Is there something else
you’re thinking about or that you’d suggest? Is there
anything on the engine you’d suggest I swap with a similar/lighter
replacement component (i.e. does anyone make a magnesium oil sump, is the swap
cost effective)? Do you know, are the Performance Engines billet aluminum
value covers significantly lighter than the stamped TCM covers, etc?
I suppose a builder could also move the ES
wing fwd a bit in an attempt to optimize the W&B, but the wing attachment
and Spar box is done by Lancair (fastbuild) and the spar integrates with the
rear seat (which is already perhaps too far fwd). Thus, he’d probably
also be designing a new wing spar and rib structure.
The other low hanging fruit is the front
gear (pun intended). Making it retract would shift 20-30 lbs rearward (in
flight only) and eliminates the weight of the fairing and pant (a couple
lbs). But, the added hydraulic system, door mechanism, and wheel well
would negate the weight savings (but it could be somewhat further aft).
However, that does not seem to be in-line with the philosophy of the ES (extra
simple). If you’re doing that you could also make the mains retract
and reduce the wing area (aka build a IV) and go faster.
Shy of those major re-configurations, it
seems I’m left with lead in the tail - and as long as I’m adding
lead in the tail, I gain some utility by putting it in plastic boxes and mixing
sulfuric acid with it {g}. Furthermore, if one of my big battery (pairs)
fails, I’m not stranded somewhere (not being able to re-start the
engine). Choosing to depart with only one working battery (pair) would be
situation dependent, but it would be an option. “Rigging” a
temporary attachment to a couple Wallmart lawn tractor batteries to “limp
home” might not be any safer.
Since a IV is theoretically similar to an
ES electrically, I am very interested in your electrical system/suggestions -
can you post/send a schematic?
Do you have a single/common ground
bus? Any special precautions with it (as a single point of
failure)? I’ve got two engine ground straps for redundancy (but
that also added several oz’s fwd of the CG) – Do you think that was
a bad tradeoff?
How is your backup alternator and battery
connected to the ships electrical systems? Through the cross-tie? Only?
Is your backup alternator a B&C
SD-20? Or equivalent?
Have you segregated your
“essential” electrical equipment (i.e. a separate E-bus) to
easily/effortlessly configure your system for low power draw (aka < 20 amps)
in the event of a primary alternator (or regulator) failure?
How do you turn on the essential bus
and/or turn off everything else?
Are there any single points of failure in
the essential bus and/or it’s feed(s)?
What equipment is on your essential bus
(if you have one)?
What is your essential bus maximum current
draw?
What is your overall maximum current draw
(everything on)? Do you have seat heaters? Front and back?
What is your typical continuous draw (with
most normal/continuous things on – like pitot heat, lights, etc
What is your strategy/timing for replacing
your batteries (every 2-3 years)? Do you have a load based AH battery
test apparatus/procedure? Do you use it as part of your annual condition
inspection? If so, at what % of total rated capacity do you replace them?
When starting, do you typically have other
electrical equipment on? EFIS? Engine Mon? GPS?
Beakon? Cabin/Panel Lights?
Have you every had a starting brownout
and/or starting spike failure? Do you believe in them?
Have you ever had issues trying to start
with a very cold battery (i.e. -10F)? What compression is your engine?
Thanks Again,
Rick